Ceramic dielectric material

ABSTRACT

A ceramic compound having the formula (La x  A +2   1-x ) 2  (Ti x  B +5   1-x ) 2  O 7  wherein A +2  is a positive divalent element selected from the group consisting of Ba, Ca, Cd, Mg, Sr and mixtures thereof and B +5  is a positive pentavalent element selected from the group consisting of Sb, Mo, Nb, Ta, W and mixtures thereof and x is a numeral ranging from 0.70 to 0.99. This compound is characterized by a relatively small temperature coefficient of permittivity, a relatively high insulation resistance, a relatively low loss factor and is compatible with relatively low cost noble metals, making it useful for forming dielectric elements in monolithic multi-layer capacitor elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to ceramic dielectric materials and somewhat moreparticularly to ceramic dielectric materials which have a smalltemperature coefficient or permittivity, a process of producing such amaterial and an electrical element formed therefrom.

2. Prior Art

During the production of monolithic ceramic multi-layer capacitors,noble metals of the platinum group are typically used to form the innerelectrodes thereof because of the high sintering temperatures andoxidizing atmosphere encountered during the production of such capacitorelements. Because the noble metals are extremely expensive (palladiumbeing the least expensive metal within this group so that it is, fromthis point of view, a preferred metal for forming inner electrodes or atleast for coating the surfaces thereof), workers in the art have madeattempts to decrease the amount of such metal required, either bydecreasing the electrode surface necessary for certain capacitors or byreducing the number of dielectric layers. A decrease in the amount ofnoble metal within a ceramic capacitor in either of the above suggestedmethods may be achieved by either increasing the permittivity value ofthe ceramic material or by reducing the dielectric layer thickness. Areducing in the thickness of a dielectric layer presupposes a higherelectrical stress of the ceramic material, since at identical operatingvoltages, a higher field strength is present in thinner dielectriclayers. Accordingly, ceramic materials having the lowest possible lossfactor, the lowest possible temperature coefficient of permittivity andthe highest possible insulation resistance are desired, provided thatthe permittivity value thereof is not overly low.

Known ceramic materials formulated on a BaO--TiO₂ --ZrO₂ basis have arelatively small temperature coefficient of permittivity and,unfortunately, have a relatively low permittivity value, ε, of about 35.Further, such known ceramic materials are sensitive to high electricalfield strengths, especially at higher operating temperatures whichapparently cause an ion migration process to occur. Over a period oftime, ion migrations lead to a gradual reduction of the dielectricresistance of such material.

Ceramic materials which have a better permittivity value (ε up to 80)are also known, however, these materials always include bismuth. Sincepalladium is not compatible with bismuth when such ceramic materials areused to form dielectric layers of a capacitor, the electrode layer mustbe at least partially formed of a more expensive noble metal.

German Pat. No. 967,609 suggests electric insulating bodies andcapacitor dielectric layers formed of a ternary system consisting oftitanium dioxide, calcium oxide and lanthanum oxide. While this materialhas a relatively high permittivity value, it also has a high temperaturecoefficient of permittivity and a relatively high loss factor.

German Auslegeschrift No. 1,005,434 suggests certain ceramic dielectricmaterials and capacitor dielectric layers made therefrom which consistsof aluminates of bismuth, of yttrium or of an element in the lanthanideseries and may include further oxide additives. However, since thismaterial includes bismuth, it is not compatible with palladium and thuscannot be used to form capacitor dielectric layers where the innerlayers are to be at least partially formed of palladium.

U.S. Pat. No. 3,400,001 suggests a ceramic dielectric material based oncalcium titanate, magnesium titanate, lanthanum oxide and neodymiumoxide combined with certain bismuth additives. Accordingly, thismaterial is also not suitable for use with palladium.

On the other hand, U.S. Pat. No. 3,431,124 or, respectively, U.S. Pat.No. 3,440,067, suggest ceramic dielectric materials based on calciumtitanate, lanthanum titanate and either magnesium titanate or,respectively, strontium titanate. While neither of these materialsinclude a bismuth additive, they are unsuitable for capacitor use sincethey exhibit relatively high temperature coefficients of theirrespective permittivities.

SUMMARY OF THE INVENTION

The invention provides certain ceramic dielectric materials which have arelatively low temperature coefficient of their permittivity and whichhave a relatively high permittivity value, a relatively low loss factorand a relatively high dielectric resistance. In addition, the ceramicmaterials of the invention are compatible with palladium so that theyare exceptionally useful for forming capacitor dielectric layers inmonolithic multi-layer capacitor elements and expensive platinum neednot be used as a coating metal for the inner electrodes while relativelyeconomical palladium may be used. The invention also provides a processfor producing ceramic dielectric materials.

Generally, the invention provides a ceramic dielectric materialconsisting essentially of a pyrochlore-type compound having the formula:

    (La.sub.X A.sup.+2.sub.1-x).sub.2 (Ti.sub.x B.sup.+5.sub.1-x).sub.2 O.sub.7 (I)

wherein A⁺² is a positive bivalent element selected from the groupconsisting of Ba, Ca, Cd, Mg, Sr and mixtures thereof; B⁺⁵ is a positivepentavalent element selected from the group consisting of Sb, Mo, Nb,Ta, W and mixtures thereof; and x is a numeral ranging from 0.70 to0.99.

In certain embodiments of the invention, the ceramic dielectricmaterials of the invention include an excess of up to about 6 atomicpercent of titanium dioxide. Further, in certain embodiments of theceramic dielectric material of the invention, up to about 30 atomicpercent of the lanthanum therein is replaced by a rare earth element,preferably neodymium.

The ceramic dielectric materials of the invention are produced by mixingselect starting materials comprised of oxides or carbonates of La andtitanium dioxide, along with select double salts yieldingg the A⁺² andB⁺⁵ elements defined hereinabove in a known manner, calcinating theresultant mixture at about 1000° to 1100° C. and then sintering thecalcinated mixture in an oxidizing atmosphere at about 1200° to 1350° C.This material is exceptionally suitable for forming dielectric elementsin an electrical capacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention provides a ceramic dielectric material characterized by arelatively low temperature coefficient of permittivity and which iscompatible with the noble metals, particularly with palladium. Theceramic dielectric materials of the invention have a relatively highpermittivity value, a relatively low loss factor and a relatively highelectrical insulation resistance (dielectric resistance). Such ceramicdielectric materials are exceptionally useful in forming capacitordielectric layers in monolithic multi-layer capacitor elements whereinrelatively low cost inner electrodes are utilized.

The ceramic dielectric materials of the invention consist of apyrochlore-type compound having the formula:

    (La.sub.x A.sup.+2.sub.1-x).sub.2 (Ti.sub.x B.sup.+5.sub.1-x).sub.2 O.sub.7 (I)

wherein

A⁺² is a positive divalent element selected from the group consisting ofBa, Ca, Cd, Mg, Sr and mixtures thereof;

B⁺⁵ is a positive pentavalent element selected from the group consistingof Sb, Mo, Nb, Ta, W and mixtures thereof; and

x is a numeral ranging from 0.70 to 0.99.

In certain embodiments of the ceramic dielectric materials of theinvention, specific materials may include an excess of up to about 6atomic percent of titanium dioxide therein. Further, in certainembodiments of the ceramic dielectric materials of the invention, up to30 atomic percent of the lanthanum therein may be replaced by a rareearth element, preferably neodymium.

The ceramic dielectric materials of the invention are useful in formingvarious electrical insulating bodies and capacitor dielectric elements,particularly in monolithic multi-layer capacitors.

The ceramic dielectric materials of the invention are produced byintermixing appropriate amounts of select starting materials, generallyoxides or carbonates of lanthanum, oxides of the rare earth elements,titanium oxide, along with niobates, tantalates, antimonates,molybdenates, or, respectively, tungstanates (B⁺⁵ element) of magnesium,barium, calcium, strontium or cadmium, (A⁺² element) calcinating theresultant mixture at about 1000° to 1100° C. and then sintering thecalcinated mixture in an oxidizing atmosphere at about 1200° to 1350° C.The mixture may be formed, as by pressing, into a desired body shapebefore or after sintering.

In order to further aid those skilled in the art in the understanding ofthe invention and the advantages thereof, a number of detailedcompositions are set forth below in Table I, which include preferredembodiments of the invention. However, the Examples are not to beconstrued as limiting the scope of the invention in any way andvariations may be made by those skilled in the art without departingfrom the spirit and scope of the invention.

Table I, below, summarizes the exemplary compositions and includes thepermittivity number, ε, the loss factor, tan δ, the insulatingresistance value, R_(is) and the temperature coefficient ofpermittivity, TK_(c), of each composition. The electrical values listedwere determined by standard measurement techniques on capacitor elementswhich had the dielectrics thereof formed of the particular ceramicmaterial shown. The TK_(c) value was determined in accordance with theprocedure suggested in IEC Publication 108, paragraph 14.5 (1967)whereby a first measurement of capacitance is made at room temperature(25° C.), a second measurement of capacitance is made at a lowerboundary temperature (in the present case at -55° C.), a thirdmeasurement of capacitance is again made at room temperature and afourth measurement of capacitance is made at an upper boundarytemperature (in the present case at +125° C.). From the temperaturecoefficients calculated from such measurements for the lower and upperboundary temperatures, a mean or average value is attained and thisvalue is listed in the Table.

Each of the sample compositions were formed by mixing togetherweighed-out amounts of select starting materials, lanthanum oxide (orlanthanum carbonate), rare earth oxides, titanium dioxide, along withniobates, tantalates, antimonates, molybdenates or tungstenates ofmagnesium, barium, calcium, strontium or cadmium, respectively. Themixtures were then calcinated in a known manner at about 1000° to 1100°C., ground to a desired particle size and formed into a desired bodyshape. These formed bodies were then sintered in an oxidizing atmosphereat about 1220° to 1350° C.

                                      TABLE I                                     __________________________________________________________________________                                                 R.sub.is                         Sample                                                                              Composition                    ε                                                                        tan δ                                                                        (Ω cm)                                                                      TK.sub.c .                   __________________________________________________________________________                                                     10.sup.6                     1   (La.sub.0.97 Mg.sub.0.03).sub.2 (Ti.sub.0.97 Nb.sub.0.03).sub.2               O.sub.7                          50 < 10.sup.-4                                                                        > 10.sup.14                                                                       60                           2   (La.sub.0.97 Mg.sub.0.03).sub.2 (Ti.sub.0.97 Ta.sub.0.03).sub.2               O.sub.7                          50 1 · 10.sup.-4                                                             >10.sup.14                                                                        55                           3   (La.sub.0.94 Mg.sub.0.06).sub.2 (Ti.sub.0.94 Ta.sub.0.06).sub.2               O.sub.7                          50 1· 10.sup.-4                                                              >10.sup.14                                                                        75                           4   (La.sub.0.90 Mg.sub.0.10).sub.2 (TiO.sub.0.90 Nb.sub.0.10).sub.2              O.sub.7                          50 5 · 10.sup.-4                                                             >10.sup.14                                                                        100                          5   (La.sub.0.97 Mg.sub.0.03).sub.2 (Ti.sub.0.97 Ta.sub.0.03).sub.2               O.sub.7 + 0.06 TiO.sub.2         50 5 · 10.sup.-4                                                             >10.sup.14                                                                        40                           6   (La.sub.0.97 Ba.sub.0.03).sub.2 (Ti.sub.0.97 Nb.sub.0.03).sub.2               O.sub.7                          51 1 · 10.sup.-                                                              >10.sup.14                                                                        20                           7   (La.sub.0.95 Ba.sub.0.05).sub.2 (TiO.sub.0.95 Nb.sub.0.05).sub.2              O.sub.7                          52 < 10.sup.-4                                                                        >10.sup.14                                                                        0                            8   (La.sub.0.93 Ba.sub.0.07).sub.2 (Ti.sub.0.93 Nb.sub.0.07).sub.2               O.sub.7                          52 1 · 10.sup.-4                                                             >10.sup.14                                                                        20                           9   (La.sub.0.92 Nd.sub.0.03 Ba.sub.0.05).sub.2 (Ti.sub.0.95 Nb.sub.0.05).        sub.2 O.sub.7                    55 1 · 10.sup.-4                                                             >10.sup.14                                                                        10                           10  (La.sub.0.90 Nd.sub.0.05 Ba.sub.0.05).sub.2 (Ti.sub.0.95 Nb.sub.0.05).        sub.2 O.sub.7                    51 2 · 10.sup.-4                                                             >10.sup.14                                                                        40                           11  (La.sub.0.85 Nd.sub.0.10 Ba.sub.0.05).sub.2 (Ti.sub.0.95 Nb.sub.0.05).        sub.2 O.sub.7                    50 < 10.sup.-4                                                                        >10.sup.14                                                                        30                           12  (La.sub.0.80 Nd.sub.0.15 Ba.sub.0.05).sub.2 (Ti.sub.0.95 Nb.sub.0.05).        sub.2 O.sub.7                    58 1 · 10.sup.-4                                                             >10.sup.14                                                                        35                           13  (La.sub.0.75 ND.sub.0.20 Ba.sub.0.05).sub.2 (Ti.sub.0.95 Nb.sub.0.05).        sub.2 O.sub.7                    53 3 · 10.sup.-4                                                             >10.sup.14                                                                        45                           14  Same as Nr. 7 +  1% Ti           53 1 · 10.sup.-4                                                             >10.sup.14                                                                        10                           15  Same as Nr. 7 + 0.5% Ti          53 1 · 10.sup.-4                                                             >10.sup.14                                                                        45                           16  Same as Nr. 7 + 1.5% Ti          53 1 · 10.sup.-4                                                             >10.sup.14                                                                        30                           17  Same as Nr. 7 + 2% Ti            53 1 · 10.sup.-4                                                             >10.sup.14                                                                        30                           18  (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 Nb.sub.0.06).sub.2               O.sub.7 + 0.04 TiO.sub.2         52 < 10.sup.-4                                                                        >10.sup.14                                                                        15                           19  (La.sub.0.93 Ba.sub.0.07).sub.2 (Ti.sub.0.95 Nb.sub.0.07).sub.2               O.sub.7 + 0.04 TiO.sub.2         52 < 10.sup.-4                                                                        >10.sup.14                                                                        15                           20  (La.sub.0.92 Ba.sub.0.08).sub.2 (Ti.sub.0.92 Nb.sub.0.08).sub.2               O.sub.7 + 0.04 TiO.sub.2         54 <10.sup.-4                                                                         >10.sup.14                                                                        -40                          21  (La.sub.0.92 Ba.sub.0.06 Ca.sub.0.02).sub.2 (Ti.sub.0.92 Nb.sub.0.08).        sub.2 O.sub.7 + 0.04 TiO.sub.2   53 < 10.sup.-4                                                                        >10.sup.14                                                                        0                            22  (La.sub.0.9 Ba.sub. 0.1).sub.2 (Ti.sub.0.9 Nb.sub.0.1).sub.2 O.sub.7          + 0.04 TiO.sub.2                 54 10.sup.-4                                                                          >10.sup.14                                                                        -30                          23  (La.sub.0.85 Ba.sub.0.15).sub.2 (Ti.sub.0.85 Nb.sub.0.15).sub.2               O.sub.7 + 0.04 TiO.sub.2         57 10.sup.-3                                                                           10.sup.14                                                                        -40                          24  (La.sub.0.925 Ba.sub.0.075).sub.2 (Ti.sub.0.925 Nb.sub.0.075).sub.2           O.sub.7 + 0.04 TiO.sub.2         52.5                                                                             5 · 10.sup.-4                                                             >10.sup.14                                                                        -60                          25  (La.sub.0.92 Mg.sub.0.08).sub.2 (TiO.sub.0.92 Nb.sub.0.08).sub.2              O.sub.7 + 0.04 TiO.sub.2         50 5 · 10.sup.-4                                                              10.sup.14                                                                        85                           26  (La.sub.0.94 Ba.sub.0.03 Ca.sub.0.03).sub.2 (Ti.sub.0.94 Nb.sub.0.06).        sub.2 O.sub.7 + 0.04 TiO.sub.2   51.5                                                                             5 · 10.sup.-4                                                              10.sup.14                                                                        35                           27  (La.sub.0.92 Ba.sub.0.04 Ca.sub.0.04).sub.2 (Ti.sub.0.92 Nb.sub.0.08).        sub.2 O.sub.7 + 0.04 TiO.sub.2   52.5                                                                             5 · 10.sup.-4                                                              10.sup.14                                                                        35                           28  (La.sub.0.94 Ba.sub.0.03 Mg.sub.0.03).sub.2 (Ti.sub.                          0.94 Nb.sub.0.06).sub.2 O.sub.7 + 0.04 TiO.sub.2                                                               53 10.sup.-4                                                                           10.sup.14                                                                        50                           29  (La.sub.0.92 Ba.sub.0.04 Mg.sub.0.04).sub.2 (Ti.sub.0.92 Nb.sub.0.08).        sub.2 O.sub.7 + 0.04 TiO.sub.2   52.5                                                                             10.sup.-4                                                                          >10.sup.14                                                                        35                           30  (La.sub.0.94 Mg.sub.0.03 Ca.sub.0.03).sub.2 (Ti.sub.0.94 Nb.sub.0.06).        sub.2 O.sub.7 + 0.04 TiO.sub.2   50 2 · 10.sup.-4                                                             >10.sup.14                                                                        80                           31  (La.sub.0.92 Mg.sub.0.04 Ca.sub.0.04).sub.2 (Ti.sub.0.92 Nb.sub.0.08).        sub.2 O.sub.7 + 0.04 TiO.sub.2   49 5 ·10.sup.-                                                                10.sup.14                                                                        95                           32  (La.sub.0.94 Mg.sub.0.02 Ca.sub.0.02 Ba.sub.0.02).sub.2 (Ti.sub.0.94          Nb.sub.0.06).sub.2 O.sub.7 + 0.04                                             TiO.sub.2                        51 2 · 10.sup.-4                                                             >10.sup.14                                                                        60                           33  (La.sub.0.92 Ba.sub.0.03 Ca.sub.0.02 Mg.sub.0.03).sub.2 (Ti.sub.0.92          Nb.sub.0.08).sub.2 O.sub.7 + 0.04                                             TiO.sub.2                        52 5 · 10.sup.-4                                                             >10.sup.4                                                                         55                           34  (La.sub.0.91 Ba.sub.0.08 Mg.sub.0.01).sub. 2 (Ti.sub.0.91 Nb.sub.0.09)        .sub.2 O.sub.7 + 0.04 TiO.sub.2  55 <10.sup.-4                                                                         >10.sup.14                                                                        -15                          35  (La.sub.0.90 Ba.sub.0.08 Mg.sub.0.02).sub.2 (Ti.sub.0.90 Nb.sub.0.10).        sub.2 O.sub.7 + 0.04 TiO.sub.2   56 2 · 10.sup.-4                                                              10.sup.14                                                                        -25                          36  (La.sub.0.89 Ba.sub.0.08 Mg.sub.0.03).sub.2 (Ti.sub.0.89 Nb.sub.0.11).        sub.2 O.sub.7 + 0.04 TiO.sub.2   56 3 · 10.sup.-4                                                             >10.sup.14                                                                        -35                          37  (La.sub.0.89 Ba.sub.0.08 Mg.sub.0.01 Ca.sub.0.02).sub.2 (Ti.sub.0.89          Nb.sub.0.11).sub.2 O.sub.7 + 0.04 TiO.sub.2                                                                    54 5 · 10.sup.-4                                                              10.sup.14                                                                        -25                          38  (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 W.sub.0.06).sub.2                O.sub.7 + 0.04 TiO.sub.2         44 <10.sup.-4                                                                         >10.sup.14                                                                        40                           39  (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 Mo.sub.0.06).sub.2               O.sub.7 + 0.04 TiO.sub.2         37 <10.sup.-4                                                                          10.sup.14                                                                        40                           40  (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 Sb.sub.0.06 ).sub.2              O.sub.7 + 0.04 TiO.sub.2         51 < 10.sup.-4                                                                        >10.sup.14                                                                        10                           41  (La.sub.0.92 Ba.sub.0.07 Mg.sub.0.01).sub.2 (Ti.sub.0.92 Nb.sub.0.08).        sub.2 O.sub.7 + 0.04 TiO.sub.2   55 < 10.sup.4                                                                         >10.sup.14                                                                        -10                          42  (La.sub.0.93 Ba.sub.0.06 Mg.sub.0.01).sub.2 (Ti.sub.0.93 Nb.sub.0.07).        sub.2 O.sub.7 + 0.04 TiO.sub.2   54 <10.sup.-4                                                                         <10.sup.14                                                                        15                           43  (La0.89 Ba.sub.0.06 Mg.sub.0.05).sub.2 (Ti.sub.0.89 Nb.sub.0.11).sub.2         O.sub.7 + 0.04 TiO.sub.2        56 < 10.sup.-4                                                                        >10.sup.14                                                                        -40                          44  (La.sub.0.87 Ba.sub.0.08 Mg.sub.0.05).sub.2 (Ti.sub.0.87 Nb.sub.0.13).        sub.2 O.sub.7 + 0.04 TiO.sub.2   57 < 10.sup.-4                                                                        >10.sup.14                                                                        -70                          45  (La.sub.0.90 Ba.sub.0.05 Mg.sub.0.05).sub.2 (Ti.sub.0.90 Nb.sub.0.1).s        ub.2 O.sub.7 + 0.04 TiO.sub.2    54 < 10.sup.-4                                                                        >10.sup.14                                                                        -10                          46  (La.sub.0.93 Cd.sub.0.06 Mg.sub.0.01).sub.2 (Ti.sub.0.93 Nb.sub.0.07).        sub.2 O.sub.7 + 0.04 TiO.sub.2   49 <10.sup.-4                                                                         >10.sup.14                                                                        60                           47  (La.sub.0.91 Ba.sub.0.06 Mg.sub.0.03).sub.2 (Ti.sub.0.91 Nb.sub.0.09).        sub.2 O.sub.7 + 0.04 TiO.sub.2   54 <10.sup.-4                                                                         >10.sup.14                                                                        0                            48  (La.sub.0.89 Ba.sub.0.04 Mg.sub.0.07).sub.2 (Ti.sub.0.89 Nb.sub.0.11).        sub.2 O.sub.7 + 0.04 TiO.sub.2   54 <10.sup.-4                                                                         >10.sup.14                                                                        -20                          49  (La.sub.0.88 Ba.sub.0.03 Mg.sub.0.09).sub.2 (Ti.sub.0.88 Nb.sub.0.12).        sub.2 O.sub.7 + 0.04 TiO.sub.2   57 <10.sup.-4                                                                         >10.sup.14                                                                        -60                          50  (La.sub.0.875 Ba.sub.0.078 Mg.sub.0.047).sub.2 (Ti.sub.0.875 Nb.sub.0.        125).sub.2 O.sub.7 + 0.04                                                     TiO.sub.2                        57 <10.sup.-4                                                                         >10.sup.14                                                                        -70                          51  (La.sub.0.85 Ba.sub.0.10 Mg.sub.0.05).sub.2 (Ti.sub.0.85 Nb.sub.0.15).        sub.2 O.sub.7 + 0.04 TiO.sub.2   60 <10.sup.-4                                                                         >10.sup.14                                                                        -150                         52  (La.sub.0.85 Ba.sub.0.08 Mg.sub.0.07).sub.2 (Ti.sub.0.85 Nb.sub.0.15).        sub.2 O.sub.7 +  0.04 TiO.sub.2  60 <10.sup.-4                                                                         >10.sup.14                                                                        -170                         53  (La.sub.0.91 Ba.sub.0.05 Mg.sub.0.04).sub.2 (Ti.sub.0.91 Nb.sub.0.09).        sub.2 O.sub.7 + 0.04 TiO.sub.2   53.5                                                                             <10.sup.-4                                                                         >10.sup.14                                                                        20                           54  (La.sub.0.90 Ba.sub.0.06 Mg.sub.0.04).sub.2 (Ti.sub.0.9 Nb.sub.0.1).su        b.2 O.sub.7 + 0.04 TiO.sub.2     55 < 10.sup.-4                                                                        >10.sup.14                                                                        -10                          55  (La.sub.0.89 Ba.sub.0.06 Mg.sub.0.05).sub.2 (Ti.sub.0.89 Nb.sub.0.11).        sub.2 O.sub.7 + 0.04 TiO.sub.2   55 <10.sup.-4                                                                         >10.sup.14                                                                        -25                          56  (La.sub.0.89 Ba.sub.0.05 Mg.sub.0.06).sub.2 (Ti.sub.0.89 Nb.sub.0.11).        sub.2 O.sub.7 + 0.04 TiO.sub.2   54.5                                                                             <10.sup.-4                                                                         >10.sup.14                                                                        -20                          57  (La.sub.0.90 Ba.sub.0.04 Mg.sub.0.06).sub.2 (Ti.sub.0.9 Nb.sub.0.1).su        b.2 O.sub.7 + 0.04 TiO.sub.2     53 <10.sup.-4                                                                         >10.sup.14                                                                        5                            58  (La.sub.0.91 Ba.sub.0.04 Mg.sub.0.05).sub.2 (Ti.sub.0.91 Nb.sub.0.09).        sub.2 O.sub.7 + 0.04 TiO.sub.2   53 < 10.sup.-4                                                                        >10.sup.14                                                                        20                           59  Same as No. 45, subjected to a lesser degree of grinding.                                                      54 <10.sup.-4                                                                         >10.sup.14                                                                        5                            __________________________________________________________________________

The advantages of ceramic dielectric materials formulated in accordancewith the principles of the invention and readily apparent from theforegoing Table. As shown, these materials are characterized byrelatively low loss factors, relatively high dielectric resistancevalues, relatively high permittivity values and a relatively lowtemperature dependence of permittivity (relatively low temperaturecoefficient of permittivity).

In order to examine process parameters, the ceramic dielectric materialof Sample No. 18 in the foregoing Table was further investigated. In oneinstance, an increasing amount of titanium dioxide surplus was utilizedwithout otherwise changing the composition and it was noted that theTK_(c) of the resulting material became progressively more negative(about -5.sup.. 10⁻⁶ per percent TiO₂). In another instance, an increasein the sintering temperature used to process Sample composition No. 18caused the TK_(c) to become more positive (about 0.6.sup.. 10⁻⁶ perdegree). In addition, a TK_(c) shift toward more negative values wasnoted with a more thorough grinding of the material (i.e., by increasingthe particle fineness). The shift of the TK_(c) value toward morenegative values was also observed when Sample compositions 45 and 59(which have substantially identical compositions) were subjected to amore thorough grinding.

Additionally, a test of field strength stress and a test of endurancestress were performed on multi-layer capacitors having ceramicdielectric elements composed of Sample compositions 1 and 18, eachformed into 30μm thick layers and were subjected to voltage loads of 200volts. After 1300 hours at 200° C. (corresponding to 260,000 hours at125° C. or 5,000,000 operating hours at 80° C.) no sign of anydeterioration of the insulation resistance was noted.

To the best of our knowledge, such field strength and endurancecapabilities have not been previously observed with known capacitordielectric elements. The combination of these characteristics along withcompatibility thereof with relatively cheap palladium and the relativelyhigh permittivity values thereof provide a decisive advantage vis-a-visknown capacitor dielectrics.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x.sbsb.1 Nd.sub.x.sbsb.2 Ba.sub.y).sub.2 (Ti.sub.x.sbsb.1.sub.+x.sbsb.2 Nb.sub.y).sub.2 O.sub.7

wherein x₁ is a numeral ranging from 0.75 to 0.92; x₂ is a numeralranging from 0.03 to 0.2 and y is a numeral equal to the sum of x₁ andx₂ subtracted from one but greater than zero.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Ba.sub.y.sbsb.1 Ca.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x₁ is a numeral ranging from 0.92 to 0.94 and y₁ and y₂ arenumerals ranging from 0.02 to 0.06 so that sum of y₁ and y₂ is equal toone minus x, with the proviso that these compounds include an excess ofup to about 5 atomic percent of titanium dioxide.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Ba.sub.y.sbsb.1 Mg.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x is a numeral ranging from 0.85 to 0.94 and y₁ and y₂ arenumerals ranging from 0.01 to 0.10 so that the sum of y₁ and y₂ is equalto one minus x, with the proviso that these compounds include an excessof up to about 5 atomic percent of titanium dioxide.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Mg.sub.y.sbsb.1 Ca.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x is a numeral ranging from 0.92 to 0.94 and y₁ and y₂ arenumerals ranging from 0.03 to 0.04 so that the sum of y₁ and y₂ is equalto 1 - x, with the proviso that these compounds include an excess of upto about 5 atomic percent of titanium dioxide.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Mg.sub.y.sbsb.1 Ba.sub.y.sbsb.2 Ca.sub.y.sbsb.3).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2.sub.+y.sbsb.3).sub.2 O.sub.7

wherein x is a numeral ranging from 0.89 to 0.94 and y₁, y₂ and y₃ arenumerals ranging from 0.01 to 0.08 so that the sum of y₁, y₂ and y₃ isequal to 1 - x, with the proviso that these compounds include an excessof up to about 5 atomic percent of titanium dioxide.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Mg.sub.1-x).sub.2 (Ti.sub.x Nb.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.90 to 0.97 and such compoundswhich also include an excess of up to about 5 atomic percent of titaniumdioxide.

Further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Mg.sub.1-x).sub.2 (Ti.sub.x Ta.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.94 to 0.97 and such compoundswhich also include an excess of up to about 6 atomic percent of titaniumdioxide.

Yet further specific embodiments of ceramic dielectric materials of theinvention comprise the following compounds:

    (La.sub.x Ba.sub.1-x).sub.2 (Ti.sub.x Nb.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.85 to 0.97 and such compoundswhich also include an excess of about 0.5 to 5 atomic percent oftitanium dioxide.

As is apparent from the foregoing specification, the present inventionis susceptible of being embodied with various alterations andmodifications which may differ particularly from those that have beendescribed in the preceding specification and description. For thisreason, it is to be fully understood that all of the foregoing isintended to be merely illustrative and is not to be construed orinterpreted as being restrictive or otherwise limiting of the presentinvention, excepting as it is set forth and defined in theheretoappendant claims.

We claim as our invention:
 1. A ceramic dielectric material having arelatively low temperature coefficient of permittivity and consisting ofa compound defined by the formula:

    (La.sub.x A.sup.+2.sub.1-x).sub.2 (Ti.sub.x B.sup.+5.sub.1-x).sub.2 O.sub.7

wherein A⁺² is a positive divalent element selected from the groupconsisting of Ba, Ca, Cd, Mg, Sr and mixtures thereof; B⁺⁵ is a positivepentavalent element selected from the group consisting of Sb, Mo, Nb,Ta, W and mixtures thereof; and x is a numeral ranging from 0.70 to0.99.
 2. A ceramic dielectric material as defined in claim 1 wherein upto about 30 atomic percent of lanthanum in said compound is replaced bya rare earth element.
 3. A ceramic dielectric material as defined inclaim 2 wherein said rare earth element is neodymium.
 4. A ceramicdielectric material as defined in claim 3 wherein said compoundcomprises:

    (La.sub.x.sbsb.1 Nd.sub.x.sbsb.2 Ba.sub.y).sub.2 (Ti.sub.x.sbsb.1.sub.+x.sbsb.2 Nb.sub.y).sub.2 O.sub.7

wherein x₁ is a numeral ranging from 0.75 to 0.92; x₂ is a numeralranging from 0.03 to 0.2; and y is a numeral equal to the sum of x₁ andx₂ subtracted from one but greater than zero.
 5. A ceramic dielectricmaterial as defined in claim 1 which includes an excess of up to about 6atomic percent of titanium dioxide.
 6. A ceramic dielectric material asdefined in claim 5 wherein up to about 30 atomic percent of lanthanum insaid compound is replaced by a rare earth element.
 7. A ceramicdielectric material as defined in claim 6 wherein said rare earthelement is neodymium.
 8. A ceramic dielectric material as defined inclaim 5 wherein said compound comprises:

    (La.sub.x Ba.sub.y.sbsb.1 Ca.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x is a numeral ranging from 0.92 to 0.94; and y₁ and y₂ arenumerals ranging from 0.02 to 0.06 so that the sum of y₁ and y₂ is equalto 1 - x; said compound including an excess of up to about 5 atomicpercent of titanium dioxide.
 9. A ceramic dielectric material as definedin claim 5 wherein said compound comprises:

    (La.sub.x Ba.sub.y.sbsb.1 Mg.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x is a numeral ranging from 0.85 to 0.94; and y₁ and y₂ arenumerals ranging from 0.01 to 0.10 so that the sum of y₁ and y₂ is equalto 1 - x; said compound including an excess of up to about 5 atomicpercent of titanium dioxide.
 10. A ceramic dielectric material asdefined in claim 5 wherein said compound comprises:

    (La.sub.x Mg.sub.y.sbsb.1 Ca.sub.y.sbsb.2).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2).sub.2 O.sub.7

wherein x is a numeral ranging from 0.92 to 0.94; and y₁ and y₂ arenumerals ranging from 0.03 to 0.04 so that the sum of y₁ and y₂ is equalto 1 - x; said compound including an excess of up to about 5 atomicpercent of titanium dioxide.
 11. A ceramic dielectric material asdefined in claim 5 wherein said compound comprises:

    (La.sub.x Mg.sub.y.sbsb.1 Ba.sub.y.sbsb.2 Ca.sub.y.sbsb.3).sub.2 (Ti.sub.x Nb.sub.y.sbsb.1.sub.+y.sbsb.2.sub.+y.sbsb.3).sub.2 O.sub.7

wherein x is a numeral ranging from 0.89 to 0.94; and y₁, y₂ and y₃ arenumerals ranging from 0.01 to 0.08 so that the sum of y₁ and y₂ and y₃is equal to one minus x; said compound including an excess of up toabout 5 atomic percent of titanium dioxide.
 12. A ceramic dielectricmaterial as defined in claim 5 wherein said compound comprises:

    (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 W.sub.0.06).sub.2 O.sub.7

said compound including an excess of about 4 atomic percent of titaniumdioxide.
 13. A ceramic dielectric material as defined in claim 5 whereinsaid compound comprises:

    (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 Mo.sub.0.06).sub.2 O.sub.7

said compound including an excess of about 4 atomic percent of titaniumdioxide.
 14. A ceramic dielectric material as defined in claim 5 whereinsaid compound comprises:

    (La.sub.0.94 Ba.sub.0.06).sub.2 (Ti.sub.0.94 Sb.sub.0.06).sub.2 O.sub.7

said compound including an excess of about 4 atomic percent of titaniumdioxide.
 15. A ceramic dielectric material as defined in claim 5 whereinsaid compound comprises:

    (La.sub.0.93 Cd.sub.0.06 Mg.sub.0.01).sub.2 (Ti.sub.0.93 Nb.sub.0.07).sub.2 O.sub.7

said compound including an excess of up to about 5 atomic percent oftitanium dioxide.
 16. A ceramic dielectric material as defined in claim1 wherein said compound comprises:

    (La.sub.x Mg.sub.1-x).sub.2 (Ti.sub.x Nb.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.90 to 0.97.
 17. A ceramicdielectric material as defined in claim 16 and including an excess of upto about 5 atomic percent of titanium dioxide.
 18. A ceramic dielectricmaterial as defined in claim 1 wherein said compound comprises:

    (La.sub.x Mg.sub.1-x).sub.2 (Ti.sub.x Ta.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.94 to 0.97.
 19. A ceramicdielectric material as defined in claim 18 and including an excess ofabout 6 atomic percent of titanium dioxide.
 20. A ceramic dielectricmaterial as defined in claim 1 wherein said compound comprises:

    (La.sub.x Ba.sub.1-x).sub.2 (Ti.sub.x Nb.sub.1-x).sub.2 O.sub.7

wherein x is a numeral ranging from 0.85 to 0.97.
 21. A ceramicdielectric material as defined in claim 20 and including an excess ofabout 0.5 to 5 atomic percent of titanium dioxide.
 22. A process forproducing a ceramic dielectric material as defined in claim 1 whereinstarting materials for said compound comprise lanthanum oxide orlanthanum carbonate, rare earth oxides, titanium dioxide and niobates,tantalates, antimonates, molybdenates and tungstenates of magnesium,barium, calcium, strontium and cadmium respectively, andcomprises:mixing select amounts of said starting materials to form asubstantially uniform mixture; calcinating said uniform mixture at about1000° to 1100° C.; grinding the calcinated mixture and forming a desiredbody shape therefrom; and sintering said formed body shapes in anoxidizing atmosphere at about 1200° to 1350° C.
 23. A dielectric elementin an electrical capacitor composed of a ceramic dielectric material asdefined in claim 1.